The present invention relates, in general, to the field of counter circuits. More particularly, the present invention relates to an integrated counter circuit particularly well suited for use with a low-power sensor.
Counter circuits, and even non-volatile counter circuits are known by those skilled in the art. Existing non-volatile counter circuits use, for example, flash memory, battery-backed memory, EEPROM or other electrically programmable non-volatile memory, as well as other technologies. Problems faced with existing non-volatile counter circuits include, but are not limited to low maximum count value and short counter life, errors due to imprinting problems, as well as limited use in low-power sensor applications due to excessive power consumption especially while the count is being updated.
A non-volatile technology that is more suited to counter circuits, especially in applications where only low power levels are provided by a sensor, is ferroelectric technology. Ferroelectric cells consume little power during reading or writing data. For low density applications such as a counter, memory cells containing two transistors and two ferroelectric capacitors, (“2T/2C”) can be used. Ferroelectric 2T/2C memory products are manufactured and sold by Ramtron International Corporation FRAM. A 2T/2C memory is also described in U.S. Pat. No. 4,873,664 entitled “Self Restoring Ferroelectric Memory”, which is also hereby incorporated by reference.
What is desired is a non-volatile counter using ferroelectric technology that solves many of the problems associated with prior art non-volatile counter circuits, and is especially well adapted to use in low-power sensor applications.